implementing an ISL in an existing fabric

I have a small fabric consisting of 5 switches in a core/edge design, however 3 of them inc the core switch are soon out of support. Is there anything to stop me implementing an ISL between 2 of the edge switches... could there be any adverse effect or risk to existing traffic in the fabric?

Due to the number of server (inc blade center NPIV ports) and storage ports I need to move onto these two switches, an ISL between the two would give me greater flexibility when planning the migrations. I plan to split the storage ports evenly between the two remaining switches and ensure all of our critical apps are connected to the same switch as the storage port it is zoned to, but in the case of some of our blade center connections this means some less important apps will need to use the ISL to connect to its own storage port.... I hope this makes sense, let me know if not...

Re: implementing an ISL in an existing fabric

Nope, this is part of the great flexibility of FC networks. You can easily add and remove switches as long as the pre-requirements are met (Unique DID, zoning db same/empty, etc). Especially if you're already using WWN zoning you can move the devices to a new SAN switch without any config changes for the device.

If you have the possibility now might be a good opportunity to create two fabrics, to increase reliability/redundancy of the SAN.